CAD oriented frequency,temperature, and DC bias dependent small‐signal,scalable circuit model of parallel‐plate paraelectric varactors

Simple, CAD compatible small‐signal scalable circuit model for the thin film parallel‐plate ferroelectric varactors is reported. It is based on the measured permittivity and loss tangent of the ferroelectric films along with the fundamental theoretical relationships of ferroelectrics in paraelectric phase. The model makes use of the measured DC field (voltage) at the inflection point of the C‐V curve where the nonlinearity (dC/dV) and the tunability are maximum. Both the capacitance and the equivalent loss resistance (dielectric losses) in the ferroelectric film take into account the low permittivity layers at the boundaries of the nano‐columns of the film. The frequency dependent losses in the top and bottom plates of the varactors and the parasitic inductance of the plates are also taken into account. The model is valid for ferroelectric films having columnar structure. It is useful in wide temperature, DC field, and frequency ranges. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.